One of the cool tricks we can use is that since the testing is all fully deterministic, once we find an interesting point in a test run - even if it is “deep” into the run time wise - our system can start many new branches of test runs off of that moment or moments just prior. So it is much more efficient than having to re-do the work to get to that rare interesting moment for each new branch.
The deterministic hypervisor is 'simple' enough albeit a pretty heavy engineering lift.